This invention had its inception as a power supply for a pinball machine. Such machines have a variety of power requirements. There are a wide variety of totalling functions to be performed, such as keeping score, counting the balls, doubling or otherwise multiplying score counts, changing ball counts with the score, etc., which are best performed by a microprocessor. In such an application, the microprocessor is a steady, low-level power consumer, demanding tight voltage regulation and isolation fron transients. Pinball machines also have a multitude of lights and solenoids which demand randomly and suddenly rather substantial power output and which are productive of strong transients. Tight voltage regulation is not imperative, but the power supply must be flexible enough and potentially powerful enough to meet the widely changing demands of these components.
Although this circuit has been devised with a pinball machine in mind, it will be appreciated that it is applicable to any situation where clean isolation between power outputs is demanded and where one of those outputs must be tightly regulated.
Switching mode power supplies are generally not new. Their advantages in terms of size and cost and efficiency of operation have been recognized and appreciated. Attention is directed to U.S. Pat. Nos. 3,740,640 to Ravis et al. dated June 19, 1973, and 3,564,393 to Williamson dated Feb. 16, 1971, and to Application Report No. B174, "Low Cost 100W Off Line Automated Switching Mode Power Supply" of the Texas Instrument Company (undated). This publication and these patents show switching mode power supplies which, however, differ from the present circuit in the specific aspects discussed.